mgr/cephadm: cephadm agent 2.0

mgr/cephadm: cephadm agent 2.0

Creates an http endpoint in mgr/cephadm to receive
http requests and an agent that can be deployed on
each host that will gather metadata on the host and
send it to the mgr/cephadm http endpoint. Should save the
cephadm mgr module a lot of time it would have to spend
repeatedly ssh-ing into each host to gather the metadata
and help performance on larger clusters.

Fixes: https://tracker.ceph.com/issues/51004
Signed-off-by: Adam King <adking@redhat.com>